Field of Invention
The present invention relates to a power system and a control method thereof.
Description of Related Art
Nowadays, a power system comprises multiple power devices whose outputs connected in parallel to constitute a redundant system. The redundant power system not only reduces the difficulty of a single power supply design, but also can reduce the risk of system crash due to a power failure.
In the redundant power system, a critical issue is how to control the start-up of the redundant power system. If one power device in the system tries to output voltage, its output current becomes large to go into an overloaded state, and a protection method must be implemented to protect the power device from damage due to overheating. There is a protection method that the power device enters a HICCUP mode during overload. A HICCUP mode, called an intermittent operation mode, means that the power device is turned on for a period of time (hereinafter referred to as Ton) and turned off for another period of time (hereinafter referred to as Toff), and then try to restart.
As more power devices in the redundant power system, Ton should be longer than Toff, so that multiple power devices can synchronously output power at the same time to start the redundant power system up. However, such a method may decrease heat dissipation performance. When the power density is increased, the limitations of this design are more severe.
In the prior HICCUP mode, Ton and Toff are fixed, and the ratio of Ton to Toff is a duty, i.e., Duty=Ton/Toff. If the duty is too low (Ton<<Toff), multiple power devices are in the HICCUP mode but fail to synchronize the output power at the same time. Thus, even if the total power of the system is less than the sum of the output powers of the two power devices, the voltage rail of the system still cannot be established and the redundant power system cannot be started up. If the duty is too high (Ton>>Toff), it is easy to achieve synchronization of the multiple power devices. With more power devices in the system, the duty should be relatively high. However, too much Ton results in poor heat dissipation performance, and increased the current stress of hardware circuit, thereby increasing the difficulty of the design.
Moreover, certain power supply topologies, such as a LLC resonant converter, have strict requirements for over-current protection mode, and therefore the duty cannot be set too high.
Accordingly, there is a need for a power system and its control method that achieves start-up control of the power system with decreased complexity, cost and size.